CNC machine tools are the core equipment of the equipment manufacturing industry, its technical level directly reflects the comprehensive strength of a country’s manufacturing industry. Since 2002, China has become the world’s largest consumer and importer of machine tools for 10 consecutive years. At present, domestic CNC machine tools in accuracy, speed, multi-axis linkage complex machining, and other high-end functions have made significant progress. However, reliability, especially in the reliability of high-end machine tools, there is still a large gap at the international level. This gap is the domestic CNC machine tools in the market competition, especially in the middle and high-end market share is low, the main reason, but also the development of the domestic machine tool industry, the technical bottleneck, needs to be resolved.

CNC machine tools a complex electro-mechanical liquid systems, and their reliability problems are more complex than traditional electronic products or mechanical structure products. With electronic products and mechanical products having established a relatively mature reliability theory and technology system is different, CNC machine tools in the reliability design and testing of technology accumulation are relatively weak. In particular, the domestic CNC machine tool reliability research started late, involving fewer organizations and personnel, and limited technical reserves, and is still in the development stage.

In industrially developed countries, such as Germany and Japan, many multinational machine tool companies have mastered the advanced and mature CNC machine tool reliability design and testing technology and will be regarded as the core competitiveness of the enterprise and the core secrets, to take strict confidentiality measures. Therefore, improving the reliability of CNC machine tools is not only a technical problem but also an important challenge for enterprise management. In this paper, we will comprehensively review and analyze the current technical status and research progress of CNC machine tool reliability from a technical point of view.

Technical progress of CNC machine tool reliability

In the mid-1970s, with the wide application of CNC machine tools in industrially developed countries and the continuous expansion of their advanced functions, the problem of machine tool failure gradually attracted the attention of the industry. Stewart B. of the British Machine Tool Industry Association used the method of on-site tracking tests to collect data on CNC machine tool failures and analyze them. In 1977, he published a report on the reliability of CNC machine tools at the Macclesfield International Reliability Conference. The report pointed out that the downtime due to failures accounted for 7.6% of the entire machine tool assessment time, and the average monthly machine tool failure occurs 1~2 times. This study reveals the importance of CNC machine tool reliability.

In 1982, the former Soviet Union scholars summarized the research and use of CNC machine tools experience, published the book “Precision and Reliability of CNC machine tools”, a systematic description of the concept of reliability of CNC machine tools, and put forward the relevant evaluation index. This book marks the early research results in the field of CNC machine tool reliability. Since then, Stewart and Plonikov’s research has laid the foundation for the international emphasis on CNC machine tool reliability technology.

In China, the Beijing Machine Tool Research Institute and the former Jilin University of Technology are the earlier institutions to research the reliability of CNC machine tools. Since the 1980s, these units began to explore the concept of CNC machine tool reliability, characterization methods, fatigue strength reliability of CNC machine tool parts, and other topics. With the gradual development of CNC machine tools in China, more and more experts and scholars have devoted themselves to the research on CNC machine tool reliability modeling and assessment, failure analysis, reliability design, testing, availability, and maintainability, and many results have been achieved.

1. CNC machine tool reliability modeling

Reliability modeling is the basis of CNC machine tool reliability assessment, analysis, and design. 1960s, the United States released the M-HDBK-217, MIL-STD-781, MIL-STD-785, and other reliability standards, which provide for the reliability of the product modeling, expectations, and test methods. These standards laid the theoretical foundation for the reliability modeling of CNC machine tools.

In 1982, Keller et al. conducted a three-year field tracking test on 35 CNC machine tools, and used the lognormal distribution and the Weibull distribution function to fit the machine tool failure interval working time, thus establishing a reliability model for CNC machine tools and estimating the machine tool’s mean time between failures (MTBF).

In China, Jilin University is the earliest unit to research the reliability modeling of CNC machine tools. In 1995, Jia et al. collected the failure data of 24 domestic CNC lathes, calculated the empirical distribution of the failure interval time by using the approximate median rank method, fitted these data by an exponential distribution, and finally established a failure interval time model of CNC lathes. In 1999, Wang et al. analyzed the 80 sets of CNC lathe failure data and found that its failure interval time can be fitted by a variety of distribution functions at a lower confidence level. Through the hypothesis testing of beta, gamma, Weibull, and lognormal distribution models, the lognormal distribution was finally selected as the best-fitting model.

The Weibull distribution is widely used in the reliability modeling of CNC machine tools because of its wide applicability. Its shape parameters can represent a variety of distribution types, such as exponential distribution, Rayleigh distribution, and so on. In their study, Dai Yi et al. found that the Weibull distribution can more accurately describe the failure interval than the exponential distribution by analyzing the failure data of a series of machining centers. Through the maximum likelihood estimation method, the parameters of the Weibull distribution are calculated, and the applicability of the model is verified through hypothesis testing. Meanwhile, the Weibull distribution is excellent in dealing with truncated data, and DAI et al. established a reliability model based on the Weibull distribution by using the residual life function, which effectively utilizes the truncated fault data resources.

As a complex electromechanical-hydraulic system, CNC machine tools have different failure rate trends at different stages of their life cycle. For such systems, a single Weibull distribution model may not be able to accurately fit the distribution of the time between failures. To overcome this problem, Chen Dingsheng et al. from Beijing University of Aeronautics and Astronautics (BUAA) proposed a two-fold Weibull segmentation model, which utilized the Weibull probabilistic paper chart analysis method for parameter estimation and verified the validity of the model through the fitting test.

However, the above model usually assumes that the machine tool failure “repair as new”, that is, the assumption that the maintenance of the machine tool is restored to the initial state, which has a certain gap with the actual situation. In this regard, Zhiming Wang et al. from Shanghai Jiaotong University proposed to model the failure time under the assumption of minimum repair using the non-hazardous Poisson process (NHPP) and boundary intensity process (BIP). The model utilizes Fisher’s information matrix method for parameter estimation, and point estimation and interval estimation are given.

Reliability tends to degrade as CNC machine tools operate for longer periods and the failure rate of a machine tool is no longer constant when it is in a period of occasional failures. Previous reliability models based only on the time between failures cannot accurately reflect this degradation process. For this reason, Yang Zhaojun et al. from Jilin University proposed a dynamic reliability modeling method that can more accurately describe the reliability level of a CNC machine tool at any moment by taking into account the time between failures and their sequence of occurrence. They modeled 18 machining centers as examples and revealed the law of its reliability change with working time.

In addition, JEFFREY et al. modeled the transient reliability of CNC machine tools by using the non-continuous-time time Markov chain (NHCTMC) and the continuous-time time semi-Markov chain (HCTSMC) methods, which provides a new way of thinking about the study of CNC machine tool reliability degradation.

In summary, the research of CNC machine tool reliability modeling has experienced the evolution from simple to complex, from assuming “repair as new” to “repair as old”, and from static model to dynamic model. These advances make the reliability model of CNC machine tools closer and closer to the actual engineering needs, for reliability design and analysis provide a solid technical basis.

2. Failure analysis of machine tools

Failure analysis is necessary for the implementation of CNC machine tool reliability growth. Domestic and foreign mainly use failure mode effects and criticality analysis (Failure mode, effects, and criticality analysis, FMECA) and fault tree analysis (Fault tree analysis, FTA), and the other two methods.

(1) FMECA of CNC machine tools

FMECA (Failure Mode, Effects, and Criticality Analysis) is a method for identifying product failure modes and evaluating their impact on product reliability, to provide a basis for eliminating or reducing the occurrence of failures. In FMECA analysis, if a hazard analysis is not performed, it is called Failure Mode and Effects Analysis (FMEA).

FMEA was first applied in the aerospace industry in the 1960s, and then the U.S. Navy and the Department of Defense formulated relevant standards in the 1970s, which widely applied and promoted the FMECA methodology. In the 1980s, Chinese scholars began to pay attention to the failure analysis methodology of CNC machine tools. In 1987, the U.S. standard of FMECA was introduced into the country, and it was applied in the national defense industry and the machinery industry.

In 1986, British scholars McGoldrick et al. analyzed the failure modes of the same types of CNC machine tools used in Britain and Turkey by distributing questionnaires to experts and operators. The study showed that the designers of CNC machine tools had insufficient knowledge of their actual operating conditions, which led to design defects as the main cause of frequent machine tool failures.

Dai Yi et al. used the traditional FMEA method to analyze the failure of vertical machining centers and made statistics from two perspectives: failure modes and failure parts. It was found that parts (components) damage accounted for 42.31% of the failure modes, liquid, vapor, and oil leakage failure modes accounted for 26.92%, and other failure modes were relatively scattered. Specifically to the parts, spindle and tool magazine failures accounted for 38.46% (of which spindle failures were mostly related to tool change operations), lubrication system failures accounted for 24.36%, Z-direction feed system failures accounted for 16.67%, and other system failures were relatively dispersed.

In the application of FMEA, the expert scores (hazard, occurrence, detection) often have subjective errors. For this reason, YANG et al. used the fuzzy affiliation function to represent the expert scores, derived the α-intercept set of risk priority coefficients through the weighted Euclidean distance algorithm, and carried out fuzzy demodeling to obtain the risk priority coefficient ranking of the failure modes.

FMECA is an extension of FMEA to further incorporate hazard analysis into the assessment process. During the failure analysis of a batch of CNC lathes, Yu Jie et al. implemented FMECA based on the application of FMEA to analyze the hazards of each failure mode and identified the CNC system and turret tool holder as the main weak points with the highest hazards (fatality). As a result, they recommended the replacement of the CNC system and improved the design of the tool holder.

The traditional FMECA methodology mainly considers factors such as the frequency of failure modes, the impact on the system, and the failure rate, but usually fails to take into account the impact of post-failure repairs on the reliability of the system. For this reason, Binbin Xu considered the impact of the degree of maintenance on the failure mode in the FMECA analysis and used the weighted Euclidean distance and the spatial diagram of the influencing factors to derive the comprehensive risk value of each failure mode, further identifying the weak points of the CNC machine tool.

In addition, Jin Yuanyuan et al. from Nanjing University of Science and Technology and Lu et al. from Dalian University of Science and Technology applied the FMECA method to the early failure screening test of chain tool magazines and manipulators and carried out the failure analysis of disk-type tool magazines and manipulators, which further extends the application scope of the FMECA method.

(2) FTA of CNC machine tools

Fault Tree Analysis (FTA) is a method of analyzing the causes of product failures using a special inverted tree-like causality diagram. Through FTA, it is possible to identify the basic causes (i.e., bottom events) that may lead to system failures (i.e., top events of the fault tree), which plays an important role in determining potential failures, conducting fault diagnosis, and reducing the probability of failures using improved design, fault monitoring, and preventive maintenance.

The FTA method was first applied to the reliability study of the missile launch system by Bell Laboratories in 1961 and achieved remarkable results. Since then, the FTA method has been rapidly developed and widely used in the international arena.

In the application of CNC machine tools, the fault tree structure is complex and the calculation volume is large, therefore, the traditional FTA method is less efficient in the calculation. For this reason, Yu Jie et al. and Chen Chuanhai and other scholars respectively adopted the Binary Decision Diagram (BDD) technology to establish the fault tree of the whole machine and hydraulic system of CNC machine tools and carried out structural importance and probabilistic importance analyses, to identify the reliability weaknesses, and to provide a basis for the subsequent improvement.

Chen Zhangrong et al. from Soochow University, on the other hand, applied FTA to the fault diagnosis of CNC machine tools. In this method, the fault tree model is stored in the computer beforehand. When the machine tool failure occurs, the computer will find the minimum cut set that may lead to the failure according to the fault information, and if there is a matching rule, the diagnostic results will be output; if there is no matching rule, the new rule will be added through manual intervention, to gradually improve the rule base.

In the actual application of FTA, often encounter the situation that the occurrence probability of the bottom event is unknown, which makes the traditional FTA method difficult to apply. To solve this problem, LI et al. used a fuzzy Markov model to establish the fault tree of the hydraulic system of CNC machine tools and used fuzzy theory to derive the uncertain information in the fault tree, to calculate the fuzzy failure rate of the hydraulic system, which provides an effective basis for the design and improvement of the reliability of CNC machine tools.

FMECA and FTA play an important role in the failure analysis of CNC machine tools. To help enterprises more efficiently use these methods for failure analysis, Jilin University’s CNC equipment reliability technology team developed a special computer software system for CNC machine tool failure analysis. The software not only manages the failure data of CNC machine tools but also realizes the functions of FMECA analysis and CNC machine tool reliability assessment, which greatly improves the analysis efficiency and accuracy.

3. Reliability design of CNC machine tools

The reliability of CNC machine tools is an inherent characteristic of product design, which is mainly determined by the design stage. However, since the current probabilistic design theory for the reliability of complex electromechanical systems is still immature, and the accumulation of data such as the load spectrum of CNC machine tools is still far from sufficient, many researchers have carried out a great deal of exploration to ensure that the expected level of reliability can be achieved at the design level. By drawing on the general product reliability design principles, the reliability of CNC machine tools has gradually formed a comprehensive design technology.

For example, the Key Laboratory of Reliability Technology for CNC Equipment in Machinery Industry of Jilin University, in conjunction with the technicians of Dalian Machine Tool Group Co. and Shenyang Machine Tool Co. jointly researched and formulated the Technical Specification for Comprehensive Design of Reliability of CNC Machine Tools. This technical specification covers many aspects such as reliability design guidelines, reliability distribution design, and reliability growth design based on failure analysis.

(1) Reliability Design Guidelines

Reliability design guidelines are a summary of reliability design experience, referring to some design principles that must be followed in the product design process to ensure product reliability. The purpose of these guidelines is to prevent designers from repeating the mistakes or design defects that have occurred in the past. The Key Laboratory of Reliability Technology for CNC Equipment in Machinery Industry of Jilin University, Shenyang Machine Tool Co., Ltd. and Dalian Machine Tool Group Co., Ltd. has integrated the principles of standardized design, simplified design, redundant design, environment-resistant design, maintainability design, safety design, and human factors design, and combined them with the product characteristics of CNC machine tools to formulate the “Reliability Design Guidelines for CNC Machine Tools”. These guidelines will be gradually improved and accumulated with the continuous advancement of design and practice.

(2) Reliability allocation design

Reliability allocation of CNC machine tools refers to the allocation of the overall reliability index of the machine tool to each subsystem according to the given guidelines and constraints. A variety of factors need to be considered in reliability allocation, including the level of technology, system importance, task requirements, maintenance, level, and so on.

For example, Wang et al. considered the impact of seven factors on reliability allocation, including failure frequency, failure fatality, failure repairability, subsystem complexity, machine tool manufacturing and assembly technology, working environment, and life cycle cost of CNC machine tools. Through the binary fuzzy allocation ratio of failure rate, the relative fuzzy allocation ratio matrix of failure rate is constructed, and the reliability allocation value of each subsystem is determined by expert scoring.

Since it is difficult to express the influence of many factors in reliability allocation with definite values, scholars such as Yang Zhaojun from Jilin University proposed the method of adopting fuzzy interval numbers instead of real numbers to express uncertain information. Combined with field test data and expert experience, they established a comprehensive reliability allocation model for CNC machine tools that integrates interval analysis, fuzzy comprehensive judgment, and hierarchical analysis methods. The model accomplishes the reliability allocation of CNC machine tools by assigning weights to factors such as failure frequency, hazard, repairability, complexity, technology level, and cost-effectiveness ratio.

In addition, Zhang Genbao et al. from Chongqing University introduced the concept of “task” in the reliability allocation of CNC machine tools. Based on the total processing tasks of CNC machine tools, they constructed a task profile hierarchical model, and used fuzzy analysis to deal with the opinions of experts in multiple fields and the risk of the research and development process, and finally realized the reliability allocation of CNC machine tools.

(3) Reliability growth design based on failure analysis

The reliability of CNC machine tools grows throughout their life cycle. The Jilin University Mechanical Industry CNC Equipment Reliability Technology Team summarizes the technical route of CNC machine tool reliability growth based on failure analysis in a block diagram. The block diagram shows two main technology lines: on the left side is the whole life cycle process of CNC machine tools, and on the right side is a series of reliability technologies implemented to match this life cycle process. Through these technologies, the reliability of a CNC machine tool can grow in cycles.

Reliability growth design based on failure analysis is the core of the CNC machine tool reliability growth technology route and has been applied and promoted in several backbone enterprises in the CNC machine tool industry.

Figure 1 Reliability growth based on failure analysis growth technology route

4. Reliability test of CNC machine tools

A reliability test is the basic work to ensure the reliability of the product, and it is the objective basis for obtaining failure data, establishing a reliability model, and conducting failure analysis and design. The reliability test of CNC machine tools can be divided into two categories: the machine tool users’ on-site reliability test and the functional components of the laboratory bench reliability test.

(1) On-site reliability test

Field test belongs to the conventional stress test, usually involving a large sample of tests, can be comprehensive, fully exposed to the fault, and truly reflect the reliability level of CNC machine tools. Field test is mainly applicable to reliability growth test and reliability assessment test. In this type of test, the machine tool is tested in the actual use environment, and it is possible to find out the possible failures of the product under specific use conditions.

However, the main drawbacks of field tests are the long test cycle, the difficult working environment, and the difficulty of fully controlling the test conditions. Since the reliability bench test facilities for CNC machine tools have not been popularized for a long time, field tests have almost become the only reliability test method for CNC machine tools. To standardize the process of field testing, Jilin University Key Laboratory of CNC Equipment Reliability Technology for Mechanical Industry has formulated the Technical Specification for Field Tests of CNC Machine Tool Reliability and conducted a large number of field tests of CNC machine tools, which has accumulated rich experience.

(2) Laboratory bench reliability test

Laboratory tests test can carry out accelerates tests and fault active excitations tests. Compared with the on-site test, the test conditions of the laboratory bench test are controllable and the test efficiency is high. This kind of test can simulate the working conditions to find potential failure problems in advance, to provide a scientific basis for improving the design and optimizing the product.

Since the 21st century, some domestic enterprises and colleges have built some key functional components of the reliability test rig, able to carry out some air rotation reliability tests. These test benches provide a more controllable and efficient testing environment for the components of CNC machine tools, which helps to assess and improve the reliability of the components in advance.

(3) Acceleration test and working condition simulation test

In 2009, the Key Laboratory of CNC Equipment Reliability Technology for the Machinery Industry of Jilin University began to develop a reliability test system for key functional components of CNC machine tools based on the basic principle of accelerated testing. The principle requires that the failure mode and failure mechanism are not changed during the accelerated test, and the basic requirements of load type, load size, load speed and frequency, and durability must be met.

Drawing on the reliability test principle and technology of automobile engines and key assemblies, Jilin University has developed a test system for key functional components of CNC machine tools with working condition simulation capability. For example, the reliability test systems of the electric spindle (Fig. 2), power servo tool holder (Fig. 3), turret tool holder (Fig. 4), disk tool magazine (Fig. 5), and chain tool magazine (Fig. 6) are equipped with electro-hydraulic servo dynamic cutting force simulation loading and dynamometer torque loading functions. Through these functions, it breaks through the limitations of the previous inability to carry out working condition simulation tests in China.

These achievements have not only solved the technical problems, but also obtained several national patent authorizations, and have been widely applied in the backbone enterprises of the machine tool industry. Through these innovative test methods, the reliability of CNC machine tools has been significantly improved, further promoting the technological progress of the entire industry.

Fig. 2 Electrospindle Reliability Test System

Fig. 3 Power servo tool holder reliability test system

Fig. 4 Reliability test system of the turret tool holder

Fig. 5 Reliability test system of disk-type tool changer

Figure 6 Chain tool changer reliability test system

5. Reliability of CNC machine tool technology development dynamics

CNC machine tool reliability technology has made significant progress in recent years, and presents the following major developments:

(1) Reliability modeling development

In the reliability modeling of CNC machine tools, the traditional “repair as old” assumption has been gradually improved to be more in line with the engineering reality of the time dynamic model. This change helps to more accurately reflect the performance degradation and failure mechanisms of equipment in the course of use and is expected to receive more attention and application in the future. This dynamic modeling method can more effectively help engineers predict the long-term reliability of machine tools and take appropriate preventive measures.

(2) Advances in Failure Analysis Methods

In the field of failure analysis, FMEA (Failure Mode and Effects Analysis) is developing into FMECA (Failure Mode, Effects, and Criticality Analysis), which not only takes into account the failure modes and their effects but also introduces the severity evaluation of the consequences of the failure, which makes the analysis results more accurate and can effectively identify the weaknesses of machine tool reliability. In addition, Fault Tree Analysis (FTA) is also widely used in computer-aided fault diagnosis of machine tools, showing its potential in intelligent fault diagnosis, especially in the automated detection and fault warning application prospects.

(3) Comprehensive development of reliability design

The reliability design of CNC machine tools is gradually forming a comprehensive design concept centered on “reliability design guidelines, reliability distribution design, and reliability growth design”. The concept emphasizes the overall reliability of the machine tool from the design stage onwards and through a reasonable design plan to allocate and adjust the reliability indicators of each subsystem, and then realize the growth and continuous improvement of reliability. The core of this approach is based on failure analysis of reliability growth technology, which will help CNC machine tools in the whole life cycle to maintain stable performance, and continuously improve its reliability level.

(4) Breakthrough in Reliability Test Technology

Regarding reliability tests, the research and development of reliability test systems for CNC machine tool functional components has become a research hotspot. In particular, test systems that can simulate real working conditions, such as electric spindles, power servo tool holders, and other key components of the test bench system, have been able to carry out more efficient acceleration test and fault excitation tests, greatly enhancing the accuracy and effectiveness of the test. At the same time, the development of accelerated test technology for functional components also makes the test cycle much shorter, thus accelerating the development and optimization of new products.

(5) Remote monitoring and intelligent development

With the intelligentization of CNC machine tools and the networking process continuing to advance, the remote monitoring of machine tool failure and early warning technology has also become an important development direction of the current CNC machine tool reliability technology. Through sensors and Internet of Things technology, CNC machine tools can monitor their operating status in real-time and upload data to the cloud platform for analysis. The fault prediction and early warning system can identify potential problems in advance to avoid the occurrence of major failures, thus effectively reducing downtime and improving the overall reliability of the equipment.

Problems in the research of machine tool reliability technology

In the research of CNC machine tool reliability technology, although significant progress has been made, it must be soberly recognized that the domestic CNC machine tool reliability technology is still in a backward state compared to industrially developed countries, there are mainly the following problems.

1. Fewer scholars and organizations in the research of CNC machine tool reliability

CNC machine tools as a failure mode, the failure mechanism is a complex and repairable system, reliability research involves several cross-disciplinary, long research cycles, capital consumption, slow results, and requires cross-sectoral cooperation. This makes the technical difficulty of CNC machine tool reliability research higher and requires long-term academic accumulation and cooperation between industry, academia, and research. However, compared with other key common technologies, the domestic CNC machine tool reliability research on the relatively small investment in science and technology, specializing in the field of scientific research institutions and research teams is scarce, and the technical system is not complete. In this regard, the relevant departments should increase investment, promote policy guidance, and strengthen the integration and cooperation of domestic research forces.

2. Weak accumulation of reliability data of CNC machine tools

The reliability data of CNC machine tools not only includes failure data but also includes maintenance data and load data. At present, the failure and maintenance data of CNC machine tools have been accumulated to a certain extent, but the accumulation of load data is seriously insufficient. The existing data are only for a certain model or a certain user, not covering a large number of CNC lathes and machining centers, and not covering different user industries, not universal. Insufficient accumulation of load data, difficulty in preparing CNC machine tools, functional components and key parts of the load spectrum, reliability design basis is not sufficient, especially can not carry out the probability of reliability design, resulting in the inherent reliability of the product level of inherent shortcomings.

3. Insufficient research on the failure mechanism of CNC machine tools

Failure mechanism research refers to the failure phenomenon through theoretical and experimental analysis to reflect the essence of the product failure of physical or chemical causes. Existing research focuses on the assumption that the failure is independent, the use of machine tool failure data for reliability modeling and assessment, and failure mode impact and hazard analysis, according to the assessment and analysis of the results of the replacement of parts and components and change the structure of the design of the improvement measures. However, due to insufficient research on the failure mechanism, the physical nature of the failure, the correlation between the failure and the common cause of the failure, and other issues are not clear, often resulting in excessive improvement and increased costs, or even ineffective improvement of the situation.

4. Heavy machine tools, light functional components

CNC machine tools are mainly composed of various types of functional components and CNC systems and support structures, so the reliability of the machine tool and the reliability of the functional components of the machine tool, especially the reliability of the key functional components are closely related. Guarantee the reliability level of functional components in Germany, Japan, Switzerland, and other developed countries in the machine tool industry to ensure the reliability of CNC machine tools is the main technical way. Domestic medium and high-grade CNC machine tools had a long time a large number of imported key functional components, the domestic machine tool functional components of the enterprise’s weak technical capabilities, most of the products are in the low-end of the low-cost competition stage makes the research institutions focus on machine tool machine.

Secondly, the reliability of the machine is usually the study of the field tracking test, does need reliability test equipment, the threshold of intervention is low; and reliability of the functional components of the study currently requires independent research and development of the functional components of the reliability of the bench test equipment, the difficulty of intervention is greater so that some researchers are discouraged.

5. CNC machine tool maintenance and availability of insufficient importance

Users in the reliability of the product’s highest demand are “to be used when that can be used”. For CNC machine tools, a typical repairable product, that is, both the requirements of its long working time between failures, but also requires its function after the failure to restore easy, short maintenance time. That is, both the requirements of its high reliability, but also requires good maintenance. At the same time to consider the reliability and maintainability of the index is the availability, also known as the broad reliability. At present, the machine tool industry, testing organizations, and scientific research indicators in the reliability of the product are still only on the reliability indicators for assessment, therefore, researchers on the maintenance of CNC machine tools and the availability of insufficient attention, although there have been articles on the study, from the point of view of meeting the needs of users of machine tools, is far from reaching the level of attention it deserves.

Conclusion and Outlook

The research on reliability technology of CNC machine tools has experienced more than 30 years and has made significant progress in the areas of reliability modeling, fault analysis, reliability design, and reliability testing of machine tools. The academic level of this field has been continuously improved, and the research results have provided technical support for the improvement of product reliability levels and product upgrading in the machine tool industry. Reliability dynamic modeling, intelligent application of fault tree, reliability of integrated design, reliability of functional components, accelerated bench test, remote monitoring of machine tool failures and failure warning, and other research hot spots in the field of CNC machine tool reliability technology.

In the obvious progress while there are still specializing in CNC machine tool reliability research scholars and institutions, CNC machine tool reliability data accumulation is weak and attaches importance to the reliability of the machine tool reliability research, the reliability of the functional components of the reliability of the research, etc., on the CNC machine tool failure mechanism, CNC machine tool maintenance and usability of the research is also not enough attention. These problems should be solved through the policy guidance of the relevant departments to attract more researchers to enter, and through the experts and scholars in this field to adjust the content of the research to be solved.

At present, CNC machine tool reliability technology has become one of the most important key technologies in the machine tool industry, to improve the reliability of CNC machine tools has become the urneedneeds of the industry. From the perspective of the development law of CNC machine tool reliability technology and industry demand for technology outlook, the main technical vision should be realized as follows.

First, we should strengthen the technical concept of full life cycle reliability, research, and development of CNC machine tools at all stages of the life cycle process reliability technology. Based on reliability testing, modeling, analysis, design, and other research, further development or strengthening of CNC machine tool manufacturing reliability, installation and commissioning reliability, early troubleshooting, transportation reliability, use of reliability, maintainability design, and preventive maintenance strategies and other reliability technology research, to provide CNC machine tools with a full life cycle of reliability assurance technology.

Secondly, we should build the reliability technology system of CNC machine tools. Through the long-term research on the reliability technology of the whole life cycle process, the research results are constantly accumulated and perfected, screened, and condensed to cover the whole life cycle of the core technology of CNC machine tools, based on which a series of CNC machine tool reliability specifications and technical standards are formulated to establish and develop a dynamic shared database of reliability technology of CNC machine tools and a failure case database, and gradually form a product reliability technology system characterized by the characteristics of the CNC machine tool industry. Product reliability technology system.

It should be pointed out that the technical demand for CNC machine tool reliability comes from enterprises, the research of technology cannot be separated from enterprises, and the application of technology is also in enterprises. Therefore, the reliability technology management system should be established in machine tool enterprises to ensure the smooth implementation of industry-university-research cooperation and the effective application of reliability technology research results in enterprises. At the same time, continue to improve the reliability of machine tool enterprises’ independent research and development capabilities, so that enterprises gradually become the main body of technology research and development of CNC machine tool reliability.